1. Field of the Invention
The present invention relates to an electrical cable coating method and an apparatus thereof for providing a coating layer on an outer surface of an electrical cable. The electrical cable has an electrically conductive core and an insulating covering layer to cover the core.
2. Related Art
An automotive vehicle is equipped with various kinds of electronic instruments. Therefore, the automotive vehicle is arranged with wiring harnesses for transmitting electrical powers from a power source and control signals from a computer to the electronic instruments. Each wiring harness has a plurality of electrical cables and connectors fitted to ends of the cables.
The electrical cable has an electrically conductive core and a covering layer made of an insulating synthetic resin for covering the core. Each connector has an electrically conductive terminal fitting and a dielectric connector housing. The terminal fitting is fitted to an end of the electrical cable to electrically connect to the core of the cable. The connector housing has a box shape to accommodate the terminal fitting.
To assemble the wiring harness, each electrical cable is cut to have an appropriate length and then a terminal fitting is fitted to an end of the cable. If desired, the cables are connected to each other. Thereafter, the terminal fitting is inserted into the connector housing to assemble the wiring harness.
Each electrical cable of the wiring harness shall be discerned in the core size, the material of the covering layer that is selected based on a heat resistance performance, and its application. The applications of the cables are systems of the vehicle such as an air bag, an anti-lock brake system (ABS) and a vehicle speed detecting system, which require electrical cables for transmitting control signals and for supplying electrical powers.
In order to discern the cables in their applications, the cables composing the wiring harness each have a stripe pattern consisting of two different colors on an outer surface of the cable. Conventionally, a colorant having a desired color is mixed with a synthetic resin material defining a covering layer of the cable, before the resin material is extruded around the core of the cable to cover the core. Then, another colorant having a color different from the desired color of the covering layer is deposited partially on an outer surface of the covering layer of the core. This provides a stripe pattern on the electrical cable.
However, a cable having such a stripe pattern has a disadvantage that the colorant deposited on the outer surface of the cable in the latter process may wear off from the outer surface with time. The wearing of the colorant is disadvantageous for discerning the stripe pattern. Thus, in a conventional improving method, the outer surface of the cable that has a stripe pattern is coated by, for example, a coating layer consisting of a transparent acrylic resin.
For example, the cable having a stripe color pattern is dipped in a coating liquid consisting of the coating material of the acrylic resin and an organic solvent for dissolving the coating material. Alternatively, the coating liquid is blasted with a high-pressure air as an aerosol on the outer surface of the cable. In addition, to improve productivity of the wring harness, the coating process to provide the coating layer on the outer surface of the cable is desirably carried out in a an assembling step of the wiring harness such as a step for cutting the wire into desired length ones.
In the step for cutting the electrical cable into the desired length ones, the electrical cable is cut after the electrical cable is fed as much as the desired length by a conveyor or the like. Thus, the moving speed of the electrical cable varies during the cutting step. The coating method, in which the electrical cable is dipped in the coating liquid, can not provide an uniform thickness of the coating layer defined on the outer surface of the cable, because the moving speed of the cable varies during the cutting step of the cable. That is, the coating layer defined on the outer surface of the cable doses not have an uniform thickness. This causes the disadvantage that the outer surface has a coating layer having a too much thickness, which is undesirable in the view of a resource saving.
Furthermore, when the coating liquid is blasted as an aerosol on an outer surface of an electrical cable, a 80 to 90% amount of the blasted coating liquid is not deposited on the outer surface of the electrical cable. This needs to blast a large amount of the coating liquid so that a coating layer having a predetermined thickness is defined on the outer surface. This is disadvantageous for saving resources thereof.
Therefore, an object of the present invention is to provide a method and an apparatus that can save resources thereof.